1. The Field of the Invention
The present invention relates generally to antenna structures coupled to mobile electronic devices. More specifically, the present invention concerns integrated antennas for portable computers.
2. The Prior State of the Art
Various communication systems are used to allow computers to communicate and exchange data and other types of information. For example, various networks, including Local Area Networks (LAN), Internet, Ethernet and conventional telephone networks, often link computers. These known communication systems, however, usually require the computer to be physically connected to telephone lines, modems or specialized wiring. In some locations, however, it is difficult if not impossible to be physically connected to the communication system. Additionally, these known systems generally cannot be used if the user is traveling or moving to different locations, as is typically the case with a laptop computer.
It is also known to use wireless or cellular telephone systems to connect laptop computers to a communication system. One such application is WLAN, part of the latest technology craze attempting to integrate wireless communication onto portable electronic devices. Another particularly effective application allowing laptop computers to communicate are cellular telephone systems, because the computer does not have to be connected to an existing telephone line. In addition, cellular telephone systems are very useful in connection with portable computers because the cellular communication circuitry can be miniaturized and provided as a component of the computer.
Both of these wireless systems often require specialized antennas. Antenna structures, predominantly used for communication, efficiently transmit and receive electromagnetic energy in the form of radio waves. Antenna structures are used whenever it is impractical, or impossible to use a physical connection, such as a transmission line or wave-guide. In order to get the best performance out of the wireless antenna, the antenna must not be obstructed by anything within its path of radiation.
Antenna design attempts to achieve good impedance matching to the feeding transmission line so as to maximize the available power for radiation. Often the power levels are limited by transmission standards. For example xe2x80x9cBluetoothxe2x80x9d wireless technology is a de facto standard, as well as a specification for small-form factor, low-cost, short-range radio links between laptops, phones, and other portable digital devices. One of the present Bluetooth specifications is to limit the transmission range to around 10meters. Bluetooth limits the transmission range by reducing the transmit power to the antenna, thus in order to conform with the Bluetooth standard the maximum available transmit power supplied to the antenna for radiation. Thus, while the antenna is designed to distribute the radiation optimally, it has a limited transmission range due to the supplied transmit power.
Antenna design also attempts to achieve the best compromise between the various constraints imposed on the desired radiation pattern. Optimization of the radiation pattern may include maximizing the radiation in one direction and suppressing it in others. If a specific desired radiation pattern is difficult or impossible to obtain using a single antenna, antenna engineers will often resort to designing arrays of simple antennas. Adjustment of the amplitude and phase of the feed voltages to the various elements in the array, as well as the geometrical arrangement of these elements, often achieves the desired radiation characteristics. Unfortunately, antenna array design is complicated by the mutual interaction between the various elements in the array and the operating environment of the array.
One example of a more difficult operating environment with multiple mutual interacting components that affect the desired radiation patterns is a laptop computer. Different brands of laptop computers use different shielding components for electromagnetic interference (EMI) that affect the antennas quite dramatically from one vendor to another. For example, some laptop computers use conductive materials or fillers, such as exotic conductive plastic material, that interfere with fully integrated antenna arrays in the laptop cases or housing bodies. Of course, the laptop display screen also presents a difficult shielding problem of the radiation pattern depending on where the antenna is located. Furthermore, a user is generally positioned in front of the laptop computer blocking a portion of the receiving area and obstructing the desired radiation pattern. Obstruction by the user is especially important with a low power wireless signal, such as Bluetooth, where signals are easy to block and absorb the radiation pattern.
Additionally, the present marketplace severely restricts the placement of integrated antenna structures on laptop computers due to performance, aesthetic, and reliability concerns. Most notable is the reluctance to place an extended integrated antenna on top of the laptop display screen, where the antenna would be virtually unobstructed out and away from everything. It is believed that this reluctance is due to concerns that the antenna structure would interfere with the LCD display. Another concern is that extended antenna structures are often bent, broken, knocked out of alignment or otherwise damaged. It is known that the repair and replacement of integrated antennas is difficult and costly. In fact, the entire attached display screen assembly is often removed and replaced instead of attempting to repair a portion of the integrated antenna or support structure. Thus, repair or replacement of the integrated antenna on top of the display screen is expensive and time consuming. As previously mentioned, even cellular systems require specialized antennas. Antennas used with cellular communication systems generally include a number of antenna elements, each including a radiating element, which is equal in length to some fraction of the wavelength to be transmitted or received. In order to increase the efficiency of communication, these known antennas must include elements that are separated by a minimum distance and these elements are preferably orientated normal to each other to provide the necessary separation and spatial diversity.
Conventional antennas used to connect a computer to a wireless communication system or cellular telephone is typically placed externally of the computer because of the noise, interference, obstruction and shielding caused by the various components of the computer. In particular, conventional antennas do not function correctly if they are obstructed or shielded by the housing or other structures of the computer.
Conventional antennas are also generally rigid and they protrude a relatively long distance from the body of the computer. These protruding antennas are often large, unwieldy, aesthetically unpleasing and they make the computer difficult to move and transport. In addition, these antennas are often bent, broken, knocked out of alignment or otherwise damaged because they can easily catch or strike foreign objects such as people, walls, doors, etc. Further, these known antennas require a large support structure to secure the antenna to the housing of the computer and this support structure requires a considerable amount of space inside the body of the computer. This space is very valuable, especially in small, portable computers. Additionally, the support structure is often damaged when the antenna is accidentally moved.
It is known that the repair and replacement of conventional antennas and the associated support structure is difficult and costly. In fact, the entire antenna assembly is often removed and replaced instead of attempting to repair a portion of the antenna or support structure. Thus, the repair and replacement of the antenna and/or antenna support structure is expensive and time consuming.
In order to alleviate these problems, known antennas are often removed before the computer is moved or transported. Additionally, known antennas must often be removed before the computer can be inserted into its carrying case. Disadvantageously, this requires additional time and resources to remove and reattach the antenna each time the computer is moved. Additionally, the antenna is often misplaced, lost or damaged when it is detached from the computer. Further, because the user often does not want to take the time and effort to remove the antenna, the computer is moved with the antenna still attached to the computer and this frequently results in the antenna being damaged or broken.
It is known to use a telescoping antenna in an attempt to minimize these problems. For example, U.S. Pat. No. 5,684,672 issued to Karidis, et al. discloses a laptop computer with an integrated multi-mode antenna. The telescoping antenna is integrated into the cover or display portion of the laptop and it outwardly extends from the display portion for use. The telescoping antenna is then retracted into the display portion when it is not in use. A coaxial cable connects the antenna to the base of the computer. In particular, the coaxial cable connects the antenna to a radio frequency (RF) adaptor card inserted into a Personal Computer Memory Card International Adapter (PCMCIA) slot in the base of the computer. Disadvantageously, the coaxial cable or connector disclosed in the Karidis patent protrudes outwardly from the base of the computer and the user must manually extend and retract the antenna. Additionally, it is well known that an antenna should usually be placed in a vertical position to obtain the optimum signal strength. This is because the antenna is most often located just above a conducting horizontal plane such as a metal desktop which acts as a reflecting ground plane that attenuates horizontal components of the electromagnetic wave. However, because the antenna disclosed in the Karidis patent is attached to the display portion of the computer and the antenna is positioned parallel to the display screen, the display screen must be vertically positioned in order for the antenna to obtain the best possible signal. The vertical positioning of the screen, however, may not be the preferred viewing angle of the screen for the computer user. Further, this and other conventional antennas have limited connectivity when the display screen is in the closed position because the antenna extends in a horizontal plane and the housing of the computer may obstruct or shield the antenna.
It is also known to connect an antenna directly to a PCMCIA card. When this type of card is inserted into the PCMCIA slot in the body of the computer, the antenna extends outwardly from the body of the computer. The PCMCIA card and the computer itself, however, are easily damaged by accidental contact with the outwardly extending antenna. Thus, users of PCMCIA cards with antennas must be extremely careful when using the computer in order to avoid damage to the card and/or computer. Additionally, these PCMCIA cards with antennas generally must be removed from the PCMCIA slot in the computer whenever it is desired to store or move the computer. This requires additional time and effort by the user, and the PCMCIA card and antenna may be lost, damaged or misplaced by the user when it is not connected to the computer.
In addition, the PCMCIA card with the attached antenna often receives a degraded or impaired signal because the antenna is frequently obstructed by the computer housing and/or shadowed by the ground plane of the display. Further, the antennas of these types of PCMCIA cards typically have a core that is very brittle and it is easily broken. If the core is broken, the PCMCIA card assembly or the antenna must be repaired or replaced.
Presently, integrated antenna diversity solutions are not found. Since two of the more popular wireless systems, Bluetooth and Home RF, are often implemented without antenna diversity; current solutions for these applications normally often use only a single antenna. These antenna solutions do not have adequate radiation coverage considering the operating environment of most digital devices. A single antenna may also be partially blocked by the operator or an object that is between the antenna and its intended point of communication. Poor coverage, mechanical reliability, extra PC cards, aesthetics, blockage of a single antenna due to an intervening object or multipath are all problems with these non-diversity solutions.
The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or completely solved by currently available antennas for portable digital devices. Thus, it is an overall object of the present invention to provide antennas that generate a radiation pattern particularly useful in reducing the noise, interference, obstruction and shielding caused by the user and various components of portable digital devices. More specifically, the present invention includes antennas that without protruding from the laptop are not obstructed or shielded by the housing or other structures of a laptop computer. Additionally, one advantage of the present invention is that it provides a diversity-like antenna solution for radios that do not support diversity, which are coupled to a portable digital device. While primarily intended for use with radios that do not support diversity, the present invention may also be used with diversity radios as well.
Accordingly, one advantage of the present invention is an integrated antenna system for a portable computer. The antenna system advantageously provides wireless or radio frequency (RF) communication with other networks or communication systems to allow data and other information to be shared or exchanged.
Another advantage of the present invention is a diversity antenna structure that accounts for the disturbance of the radiation pattern by the laptop and the surrounding environment. A diversity antenna structure may be connected to a diversity radio, such as those used in IEEE 802.11 systems, that decide which of the antennas is receiving the strongest signal, and thereby ensure the best possible link performance. Non-diversity radios, such as those used in the Bluetooth systems, are also able to use the diversity antenna structure of the present invention via a power divider, which re-characterizes the diversity antenna as the single antenna expected by the non-diversity radio. More specifically, the present invention supplies an integrated diversity antenna solution that may also be used with non-diversity based wireless systems.
Yet another advantage of the present invention is the mechanical reliability, omnidirectional radiation pattern coverage, and aesthetically unobtrusive nature of the integrated wireless system. The integrated wireless system comprises a mini PCI card or integrated printed circuit board (PCB) with a radio transceiver, power divider, and preamplifier. The system further comprises at least two antennas connected to the PCI card or PCB via mini-coaxial cables. The various electrical couplings between the mini PCI card and at least two antennas can be electrically isolated to improve the signal strength and minimize signal blockage due to the presence of an intervening object.
In a preferred embodiment of the present invention, the apparatus allows wireless communication between a portable computer and a communications network to be established. The apparatus includes a portable computer with a base unit having housing with an upper surface, a lower surface and side walls. The portable computer also includes a display unit, which is attached to the base unit and the portable computer is movable into an open position and a closed position. At least two antennas are enclosed within the side walls of the housing on the base unit of the portable computer. The at least two antennas are configured to transceive diversity and non-diversity wireless communications. Desirably, the at least two antennas are surface mounted antennas, such as, but not limited to, patch antennas that produce a radiation pattern that does not interfere with the radiation pattern of the partner antennas. In the case of a dual antenna structure each antenna would produce a kidney or cardioid shaped radiation coverage and tend to fill the space from the middle of the portable computer outward. Alternatively, the at least two antennas may be overmolded surface mounted antennas placed in the seam of the housing such that the surface of the overmolded antennas are flush with the upper surface and lower surface of the housing along the side walls of the housing. This configuration exposes the at least two antennas to the exterior, thereby reducing the interference, without causing the antennas to protrude from the housing and subject them to undo risk of damage. Both of these configurations increase the reliability of apparatus by removing any moving breakable parts normally associated with antennas. The antennas are operable regardless of the position of the display unit attached to the base unit.
The apparatus also includes a power divider feed structure connected to orthogonally configured antennas via micro-coax cable. Desirably, the power divider feed structure is configured to automatically feed the at least two antennas to produce an omnidirectional radiation coverage pattern, regardless of attached radio. Thus if the portable computer is using a non-diversity radio, such as the radio used in a Bluetooth system, the apparatus utilizes multiple antennas by feeding the radio from the power divider feed structure. But if a diversity radio, such as those used in the IEEE 802.11 RF systems, is used then the apparatus would decide which of the antennas is receiving the strongest RF signal to ensure the high RF link performance. An exemplary power feed structure includes a Wilkinson power divider integrated onto a printed circuit board (PCB). Alternatively, the apparatus can utilize a branch-line quadrature hybrid power divider.
In another preferred embodiment, the present invention includes a portable computer having an open position and a closed position. The portable computer includes a base unit with an upper surface, a lower surface and at least two side walls; at least four orthogonally located patch antennas are connected to the base unit and configured to establish wireless communication between the portable computer and a wireless communication system; and a power divider feed structure is configured to transceive signals with the antennas. The antennas are located in the recess of the seam of the base unit, preferably along the side walls. This configuration allows for spherical radiation coverage regardless of the position of the computer, but also results in a power loss of 6 dB instead of the 3 dB loss observed from a dual patch antenna configuration. Additional interference circuitry is included in the apparatus to coordinate reception from each antenna, since the patch antenna patterns would not be totally orthogonal the signals from the antennas might sum together at an intended destination to form constructive and destructive interference in certain directions.
The present invention, in yet another preferred embodiment, is an antenna system for use with a portable computer having a base unit with a recess sized and configured to receive the antenna system. The antennas used within the antenna system include a radiating element, dielectric material, and a ground plane. The radiating element and ground plane of each antenna are electrically connected via micro-coax cable to a connector of the power divider configured to attach multiple antennas to a radio on a portable computer. The radio may be a wireless or RF radio, integrated into the portable computer. The antenna system is positioned within the seam in the molding on the base unit. The radiating element of the antenna may include a plurality of elongated members positioned proximate to each other. A dielectric material separates these elongated members, but the members are spaced close enough to create a monopole or dipole antenna.
Advantageously, the antenna system of the present invention is a small, compact antenna array that does not protrude from the housing of the computer. Accordingly, the antenna system has little effect on existing portable computer designs and it requires only a small space inside the computer housing. In this location the antennas are not subject to the same exposure risks encountered by extended antenna structures. This significantly decreases design and manufacturing costs while increasing the reliability of the antenna system. The diversity of using two patch antennas, one on each side, of the digital device creates two hemispherical radiation patterns with a minimally sized null area between the antennas. The present invention can connect the two antennas back to a non-diversity transceiver through a power-combiner so that the overall structure appears as a single antenna. This feature allows the antenna structure flexibility to be integrated right into the clamshell housing on the laptop for easier manufacture because the antenna structure can be used with both types of wireless radios. Furthermore, the user would not be aware of where the digital device obtained its wireless conductivity.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.